1. Field of the Invention
The present invention relates to an image pickup optical system and a camera having it, and for example, it is suitable for a digital still camera, a video camera, a silver halide photographic camera, etc.
2. Related Background Art
Heretofore, in imaging apparatuses such as a silver halide photographic camera, a video camera, and a digital still camera, there is an article, called a macro lens or a micro lens (hereinafter referred to as “macro lens”), among image pickup optical systems mainly used for image pickup of short distance objects.
In the macro lens, in high magnification, a taken image deteriorates largely since the taken image blurs significantly by the vibration of an imaging system. In addition, since the depth of field becomes extremely small in high magnification image pickup, it becomes frequent to take an image with stopping down (enlarging f-number). Hence, since exposure time becomes long inevitably, it becomes easy to receive the influence of the vibration of the imaging system. For this reason, when an image is taken with a macro lens in high magnification, it becomes necessary to perform correction lest the displacement of a taken image, that is, so-called a blur of the taken image should arise even when the imaging system vibrates.
In the macro lens, a vibration reduction optical system having a vibration reduction function, which prevents a blur of a taken image, is known (Japanese Patent Application Laid-Open No. H7-294853 (counterpart: U.S. Pat. No. 5,598,299), and Japanese Patent Application Laid-Open No. H9-197265 (counterpart: U.S. Pat. No. 5,825,546)). In Japanese Patent Application Laid-Open No. H7-294853, at the time of focusing on a object in a short distance, the short distance image pickup in a life-size is performed by a system of making a front part of a lens system zoom in toward an object, and vibration reduction is achieved by moving a part of a lens unit, which is fixed during focusing, to a direction orthogonal to an optical axis.
In addition, in Japanese Patent Application Laid-Open No. H9-197265, inner focusing that the overall length of a lens system is constant during focusing is adapted to perform the vibration reduction by moving a part of the lens unit, which is the nearest to an image and is fixed during focusing, to a direction orthogonal to an optical axis.
Generally, in a mechanism to obtain a static image by canceling a displacement of a taken image due to the vibration of some lens units of an imaging system, it is required that a correction amount of the displacement of an image is large, and that a movement amount of the lens unit (movable lens unit) driven for the correction of the displacement of the image is small.
In addition, if many eccentric aberrations such as eccentric coma aberration, eccentric astigmatism, eccentric chromatic aberration, and eccentric field curvature aberration arise by decentering the movable lens unit, a taken image blurs because of the eccentric aberration when the displacement of an image is corrected. For example, when many eccentric distortion aberrations arise, a movement amount of a taken image on an optical axis and a movement amount of the taken image of a peripheral part of an image plane, with respect to a single movement amount of the moving lens unit, differ. Hence, when the moving lens unit is decentered so as to correct the displacement of the taken image on the optical axis, a phenomenon equivalent to the displacement of the image arises in the peripheral part of the image plane, and hence, it causes the deterioration of the optical characteristics remarkably.
In this way, in an optical system having a vibration reduction function, so as to reduce the deterioration of image quality with the movable lens unit in an eccentric state by moving the movable lens unit, and to downsize an entire apparatus, it is required that not only an amount of emergence of an eccentric aberration is small, but also so-called eccentricity sensitivity is large. Here, the eccentricity sensitivity denotes a degree of capability to correct a large displacement of an image with a small amount of the movement of the movable lens unit, and is represented as a ratio Δx/ΔH where Δx denotes a correction amount of the displacement of an image, and ΔH demotes a unit amount of movement of the movable lens unit.
In addition, as a lens type of the macro lens, heretofore, a symmetrical lens type (so-called Gaussian type) or an approximately symmetrical lens type has been used in many cases. In these lens types, since the focusing on from an infinite object to a short distance object is performed by moving the entire lens unit or some lens unit toward an object side, overall lens unit length changes. Therefore, these lens types are disadvantageous at the point of user-friendliness in comparison with an inner focus type that overall lens unit length is constant.
Furthermore, in an inner focusing type macro lens, in view of a mechanism, it is difficult for the focusing lens unit for focusing on short distance objects, to have the construction of providing a function as a movable lens unit for the correction of the displacement of an image since the mechanical structure is upsized and becomes complicated. Moreover, also in the configuration of the lens unit, which is fixed during focusing, to be a movable lens unit for correcting the displacement of an image, it becomes important to obtain a large displacement amount in a small movement amount of the movable lens unit in a direction orthogonal to the optical axis.